This invention relates to a motor power assisted vehicle and more particularly to an improved sensor and control arrangement for said vehicles.
An increasingly popular type of vehicle is one which is designed so as to primarily operated by the power of the user. Examples of this type of vehicle are power assisted bicycles and wheelchairs. The primary motive power for the vehicle is, as with purely manually powered vehicles, the manual input force of the rider.
However, in order to make these vehicles more accessible and available, particularly by people who might not otherwise be able to use them, it has been proposed to provide an assist motor that will augment the manual power under some circumstances. These types of devices generally use some form of input force sensors so as to sense the amount of manual input force applied by the vehicle rider or operator. Then, a motor assist is provided which adds to the manual force in some ratio so as to permit the user to have this assist. Because the amount of power assist is based upon the amount of manual force applied, it is not likely that the vehicle will overspeed or that the rider can loose control of the vehicle.
Obviously, therefore, it is necessary for these vehicles to have a very effective and also sensitive mechanism that senses the manual force input by the operator. One common way this is done is to couple the manually operated driving member of the vehicle to the driven element, such as a driven wheel, through a planetary transmission. The braked member of the planetary transmission, normally the sun gear, is permitted to rotate slightly with a spring bias resisting this rotation. Thus, by determining the amount of deflection of the spring and rotation of the normally braked gear it is possible to measure the manual force input. This provides a very effective and relatively simple type of force sensor.
With this type of vehicle, however, there are some disadvantages particularly relating to the force sensors. Since the force sensor is associated with the transmission that couples the manual power to the driving component of the vehicle, the sensor and its components must be of sufficient strength and size so as to accommodate all of the driving loads. This makes the mechanism rather bulky and requires all elements of the sensing mechanism to have adequate strength to provide the transmission of power. Thus, it is frequently necessary to employ materials in the entire transmission that have high rigidity and frequently heat treated gears having substantial widths and diameters are employed.
In addition to the cost disadvantage, it must also be remembered that this type of vehicle is primarily an adaptation of a purely manually operated vehicle. That is, in order to save cost and components it is desirable if the basic vehicle can be substantially the same as its purely manually powered counterpart and only modified to the minimum extent necessary to accommodate the power assist components.
However, when large transmissions and force sensors are employed, this makes the structure more expensive and more cumbersome. In addition, the placement of the components with this type of mechanism is somewhat dictated by the location of the driving transmission and thus, space utilization is deteriorated.
In addition to these difficulties, the assist mode frequently drives the vehicle through at least part of a common transmission with the manual drive. This further makes the system more complicated and more difficult to incorporate into a conventional vehicle structure.
It is, therefore, a principal object of this invention to provide an improved, simplified and low cost force sensor for a power assisted manually operated vehicle.
It is a further object of this invention to provide a force sensor for sensing the manual force input to such a vehicle with a relatively simple, low cost structure and one which can be placed at a wide variety of locations without substantial modification of the basic vehicle.
It is a further object of this invention to provide an improved, simplified and low cost force sensor for sensing the manual force applied to a vehicle without the necessity of having the force sensor mechanism being robust enough to transmit the driving load for the vehicle.
This invention is adapted to be embodied in a power assisted manually powered vehicle having at least one driving wheel. An operator driven driving member to which an operator applies a manual force is provided. A first transmission couples this driving member to the driven wheel for operator power driving of the vehicle. An assist motor is provided for exerting a driving force to the vehicle through a second transmission. A differential transmission is connected between the operator driven driving member and the driving wheel for providing a signal indicative of a change in phase between the operator driven driving member and the driving wheel. A phase change sensor is associated with the differential transmission for providing a signal indicative of the change in phase. Control means are responsive to the output signal of the phase change sensor for supplying an amount of power from the assist motor for assisting in the driving of the vehicle.